IRS1 Regulation by Wnt/β-Catenin Signaling and Varied Contribution of IRS1 to the Neoplastic Phenotype

Guido T Bommer,Ying Feng,Ayaka Iura,Thomas J Giordano,Rork Kuick,Hüseyin Kadikoy,Deanna Sikorski,Rong Wu,Kathleen R Cho,Eric R Fearon

doi:10.1074/jbc.m109.060319

Guido T Bommer, Ying Feng + Show 8 more

Open Access

https://doi.org/10.1074/jbc.m109.060319

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Abstract

Dysregulation of β-catenin levels and localization and constitutive activation of β-catenin/TCF (T cell factor)-regulated gene expression occur in many cancers, including the majority of colorectal carcinomas and a subset of ovarian endometrioid adenocarcinomas. Based on the results of microarray-based gene expression profiling we found the insulin receptor substrate 1 (IRS1) gene as one of the most highly up-regulated genes upon ectopic expression of a mutant, constitutively active form of β-catenin in the rat kidney epithelial cell line RK3E. We demonstrate expression of IRS1 can be directly activated by β-catenin, likely in part via β-catenin/TCF binding to TCF consensus binding elements located in the first intron and downstream of the IRS1 transcriptional start site. Consistent with the proposal that β-catenin is an important regulator of IRS1 expression in vivo, we observed that IRS1 is highly expressed in many cancers with constitutive stabilization of β-catenin, such as colorectal carcinomas and ovarian endometrioid adenocarcinomas. Using a short hairpin RNA approach to abrogate IRS1 expression and function, we found that IRS1 function is required for efficient de novo neoplastic transformation by β-catenin in RK3E cells. Our findings add to the growing body of data implicating IRS1 as a critical signaling component in cancer development and progression.

Highlights

With the AXIN and APC tumor suppressor proteins and other factors to phosphorylate ␤-catenin at defined serine and threonine residues in its amino (N)terminal domain
Among the genes expressed at higher levels in cell lines with activated ␤-catenin, we further investigated the gene for insulin receptor substrate 1 (IRS1)
Significant increases in the Irs1 gene and protein expression were observed in S33Y-␤-catenin and WT-␥-catenin transformed RK3E lines as well as RK3E cells transformed by GLI (Fig. 1, A and B) [27]

Summary

Introduction

With the AXIN and APC (adenomatous polyposis coli) tumor suppressor proteins and other factors to phosphorylate ␤-catenin at defined serine and threonine residues in its amino (N)terminal domain. To pursue further the role of the Wnt/␤catenin pathway in activating Irs1 expression, we analyzed the expression of IRS1 in derivatives of the RK3E cell line that were neoplastically transformed by selected genes, including S33Y␤-catenin, wild-type ␥-catenin, GLI1, MYC, and an oncogenic KRAS cDNA (G12V-K-Ras).

Results

Conclusion